Drill fracture detection by integrating disturbance observer and rotational digital filter

• Sensor-less tool fracture detection applying disturbance observer is proposed.
• A rotational digital filter theory to enhance the detection accuracy is developed.
• The developed filter is applied to an estimated cutting force in x- and y-axis.
• Large spectrum density is observed only in drilling with fractured tools.
• Drills with more than 1 mm2 fracture can be discriminated by the proposed method.

Tool fracture detection is important to avoid tool breakage and ensure cutting accuracy. However, conventional tool condition monitoring methods use additional sensors that are expensive, increase the failure rate, and reduce the machine-tool stiffness. This study proposes a novel in-process method to detect tool fracture based on disturbance observer theory. It uses only servo information in a ballscrew-driven stage control system. Furthermore, a rotational digital filter is developed and applied to drilling tests to enhance the detection accuracy. Tool fracture is successfully detected without any external sensors by the proposed method.